I don't know whether any of mine got eaten but the first spawn my female guppy delievered was 8. I wasn't sure how long the pregnacy was going to last so she spawned them in my community tank. I have heard that they can spawn up to about 20 or so. I think the 8 survived beacause I had some leaves floating on the suface for them to hided in until they got big enough to fend for themselves.
if shes a pet shop guppy then theres no garantee (sp?) that this will be her first lot of fry, generally it also depends on the size and age of the female eg one of my larger females had 30 in her first brood whereas a smaller female had 5